Anchor-slot waveguide coupling aperture



Jan. 18, 1966 R. R. KlNSEY ANCHOR-SLOT WAVEGUIDE COUPLING APERTURE Filed Dec. 30, 1965 F \w d J N ||l| n I Wm H S MSAT UTUL GIS F EDTR V A 0 s F F w w M F WEM TRSA F F m l- S I- L T E w m S B M H U D m 0 L .L S s R m m. ,1 w D M m N T U C o E R R WEDGE'ENDSLOT ANCHORSLOT INVENTOR RICHARD R. KINSEY- HIS ATTORNEY.

United States Patent 3,230,483 ANCHOR-SLOT WAVEGUIDE COUPLING APERTURE Richard R. Kinsey, Cazenovia, N.Y., assignor to General Electric'Company, a corporation of New York Filed Dec. 30, 1963, Ser. No. 334,169 Claims. (Cl. 33310) This invention relates to RF coupling devices and in particular to apertures of use in coupling RF signals from one side of a conducting wall to another.

Many devices have been made for coupling radio frequency signals between one transmission line and another or between an antenna and free space. Among the more useful of these have been open orifices which have included slots cut .through walls to afford a linkage for the RF electromagnetic fields. Generally speaking, coupling through such orifices is defined in terms of power attenuation, in decibels. A related characteristic is called directivity and also is expressed in decibels. Power attenuation generally decreases for a selected bandwidth of signals with increases in slot length. Directivity, in general, is a function of spacing between the slots and of the relative location of the slots and refers to the ratio of power transmitted in the desired direction in a waveguide to that in the undesired direction. A limit to the length of the slots, and to possible increases in power coupling of a broadband signal through changed slot length, is imposed by the size of the waveguide junction, or the coupling region, where the transfer of energy is to take place.

One way to increase coupling, while maintaining high directivity between signals in cross-coupled waveguides, has been to cross two slots in each of two diagonally opposite quadrants of the coupling region in order to more effectively utilize the space available. At the lower end of frequency bands of interest, however, the coupling slots will frequently become very small in terms of a wavelength even with the slots lengthened to the boundary of the coupling region. When used with reduced size waveguides, especially with ridge waveguides which are otherwise desirable, the maximum coupling through such crossed-slots in a particular instance has been found to be only db, i.e., attenuation is 15 db, under circumstances in which .much higher coupling is required. Attempts to increase coupling of such crossed slots have included the use of circular openings at the ends of the slots to form dumb-bell slots. These dumb-bell slots have produced some increases in coupling. However, in common with other more elaborate orifices which have been proposed they are difficult to design for different coupling values, they are onerous to manufacture with automatic machines, and they tend to be so frequency sensitive that they cannot transmit signals of adequate bandwidth without large variations in coupling.

It is, therefore, a primary object of this invention to provide radio frequency couplers with apertures having a geometry which can be easily adjusted to transmit different fractions of available power over a broad bandwidth.

It is another object of this invention to provide an improved RF coupler which may be more readily produced by automatic machining methods.

3,230,483 Patented Jan. 18, 1966 It is still another object of this invention to provide a waveguide coupler with a lower Q than earlier devices and consequently with coupling capacity which is less frequency sensitive.

This invention relates to improved couplers for coupling RF signals between a waveguide and space outside the waveguide, where the outside space may be another waveguide, the half-space of an antenna, or some other load. The couplers commonly will comprise orifices composed of crossed slots with anchor-shaped terminals, but single slots may also be used.

Novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of a specific embodiment when read in connection with the accompanying drawings in which FIG. 1 illustrates some geometrical considerations of one embodiment of the invention, FIG. 2 illustrates an embodiment of the invention, FIG. 3 shows certain relationships characteristic of embodiments of the invention and FIG. 4 depicts certain analogies between ridged waveguides and. coupling slots.

Turning first to FIG. 1, there are illustrated some aspects of the geometry relating to cross coupled waveguides, with waveguides at 2 and 4 shown in elevation. The shaded areas in the figure labeled spaces available for coupling apertures in the common bnoadwall are determined in accordance with theory and experience which indicate that suitable orifices in these areas can provide the desired directivity. For example, the principal path of signals received via waveguide -2 from the direction included by the arrow A through suitable coupling apertures in the shaded areas would be out through 'waveguide 4, as indicated by arrow B. If coupling apertures had been placed in the unshaded quadrants of the space, a signal from waveguide 2 would be directed downward into waveguide 4 as indicated by the dotted arrow C. The reason for this directivity, of course, is that while a signal arriving from direction A couples signals in both B and C directions, in the case of signals originating through orifices in the shaded areas the paths of the signals originating through each orifice are of equal length in the C direction but excited out of phase and cancel while, ideally, the path lengths differ by one-half wavelength in B direction and thus compensate for the 180 excitation phase difference so that they add. The same principle applies to signals induced in the second waveguide through orifices in the unshaded areas, but the direction traveled by the output signals would be reversed.

FIG. 2 shows waveguide 4 in position with the waveguide 2 removed to disclose an embodiment of the invention. An attractive geometrical feature of the invention, when it is used in a directional cross-guide coupler, can be seen in FIG. 2 The coupling available through slots (which will be referred to as anchor slots) made in the form shown can be varied by adjusting the length of the fluke arms F. This is the case, since adjustments in the length of the fluke arms have an effect similar to changing the length of the crossed arms G which in turn affects the resonant wavelength. Examples of the elfect on coupling of changes in the length of the fluke arms can be seen for particular waveguides in FIG. 3.

In order to provide a clearer understanding of the nature and scope of this invention, attention is directed to FIG. 4 which shows the development of these slots by analogy with ridge waveguide. Picture the slots shown in FIG. 4 as very short lengths of various waveguide crosssections. It is apparent that the dumb-bell slot can be considered to be a rounded-end slot with ridges added. Likewise, the H-slot can be considered to be a rectangular slot with rectangular ridges. By analogy, the anchor slot of the present invention can be regarded as a wedge-end slot with ridges of the shape shown.

Considering the anchor slot in terms of the analogy presented in the last paragraph, it is clear that some considerations useful in the design of ridge waveguides can be applied to the anchor slot. For example, changes in the depth of the ridge will change the resonant (cutoff) wavelength of ridge waveguide. With the anchor slot, changes in depth of the ridge are made by easily machined changes in the length of the fluke arms. Examples of the results of changes in the length of the fluke arms are shown in FIG. 3 for a 5 db range in coupling. It will be appreciated that single ridge slots rather than double ridge slots, as shown in FIG. 4 may be used in the practice of the invention, just as a single ridge is commonly used with ridge waveguide.

Comparisons of the anchor slots of the present invention with dumb-bell slots, which seem more like the present invention than other prior art, have indicated that anchor slot coupling apertures provide roughly 6 db more coupling than do dumb-bell slots having the same slot width. To achieve equal coupling, the width of dumb-bell slots would need to be decreased. Since the Q varies inversely as the square root of slot width, the effect of reducing the slot width is to increase the he quency sensitivity to an undersirable extent.

The foregoing has been directed chiefly to describing the application of the invention as a directional coupler between crossed Waveguides. It will be recognized that the invention can be used to advantage in other types of waveguide couplers where high magnetic polarizabilities are desired in a coupling aperture of small length. It may be applied, for example, to such uses as coupling between waveguides aligned in parallel. It may also be applied to slot antennas. The application of the invention to antennas incorporating arrays of slots is particularly promising in view of the superior control of resonance now possible for slots made in accordance with the principles of the invention. TEM line arrays and edge slot arrays, for example, are both applications in which a loaded slot capable of high resonant conductance and low Q is desired.

Although the invention has been described with respect to certain embodiments, it will be appreciated that many modifications and changes may be made by those skilled in the art without departing from the spirit of the invention. It is intended, therefore, by the appended claims, to cover all such modifications and changes as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A radio frequency coupler to enable the transfer of RF energy through a conductor wall of a waveguide comprising,

a slot cut through the conductor wall, said slot defining the base of a triangle shaped area, and

each end of the slot terminating in an additional relatively shorter slot cut through the conductor, each of said additional slots extending parallel to an arm of the triangle shaped area, but terminating short of the apex thereof,

all said slots throughout their lengths being open to the space within the waveguide for RF energy trans fer between said space and that outside the waveguide. 2. A radio frequency coupler to enable the transfer of 5 RF energy through a conductor wall of a Waveguide comprising,

a slot cut through the conductor wall, said slot defining a diagonal between opposite corners of a parallelogram, and each end of the slot terminating in additional slots cut 10 through the conductor, said additional slots being parallel to and shorter than the sides of the parallelogram, all said slots throughout their lengths being open to the space within the waveguide for RF energy transfer between said space and that outside the waveguide.

3. A radio frequency coupler to enable the transfer of RF energy through a conductor wall of a waveguide comprising,

a principal slot cut through a conductor wall,

each end of the slot relatively shorter than said principal slot and terminating in additional slots having shapes substantially like that of the fluke of an anchor, where each of the additional slots has a Width substantially equal to that of the principal slot, all said slots throughout their lengths being open to the space within the waveguide for RF energy transfer between said space and that outside the waveguide.

4. A radio frequency coupler to enable the transfer of RF energy through a conductor wall of a waveguide comprising,

a pair of slots cut through the conductor wall, said slots crossing at right angles at the center of a parallelogram shaped area in said conductor wall and extending to the corners of the parallelogram shaped area, and

the terminus of each slot including cuts through the conductor wall providing two slot extensions each parallel to but shorter than one of the sides of said parallelogram shaped area, all said slots throughout their lengths being open to the space within the waveguide for RF energy transfer between said space and that outside the waveguide.

r 5. A radio frequency coupler substantially as claimed in claim 4 in which the parallelogram shaped area is equilateral.

6. A radio frequency coupler substantially as claimed in claim 4 in which the parallelogram shaped area is square.

7. A radio frequency coupler substantially as claimed in claim 4 in which the slots parallel to the sides of said parallelogram shaped area are extended for equal distances.

8. A radio frequency coupler to enable the transfer of RF energy through a conducting wall of a waveguide comprising,

a plurality of slots cut through the conducting wall,

each of said slots being cut to extend radially from a central point, and

6O terminal slots relatively shorter than said slots cut to extend from the outer end of each slot, each terminal slot extending in the manner of the fluke arm of an anchor to increase coupling through said slots, all

said slots throughout their lengths being open to the space within the waveguide for RF energy transfer between said space and that outside the waveguide. 9. Means for transferring radio frequency electromagnetic energy from one transmission line to another having a length of common wall comprising,

at least one aperture piercing common wall between said transmission lines and said aperture including slots emanating radially from a central point,

7 terminal slots relatively shorter than said radially emanating slots cut to extend from the outer ends of each thereof, each terminal slot extending in the manner of the fluke arm of an anchor to increase coupling between the transmission lines through said slots.

10. Means for transfering radio frequency electromagnetic energy substantially as claimed in claim 9 in Which the transmission lines are waveguides oriented perpendicular to each other and tWo of said apertures are provided in diagonally opposite quadrants of a four quadrant area of said common Wall between the perpendicular waveguides so as to serve as directional cross-guide couplers.

References Cited by the Examiner UNITED STATES PATENTS References Cited by the Applicant UNITED STATES PATENTS 2 602,859 7/1952 Moreno.

HERMAN KARL SAALBACH, Primary Examiner. 

1. A RADIO FREQUENCY COUPLER TO ENABLE THE TRANSFER OF RF ENERGY THROUGH A CONDUCTOR WALL OF A WAVEGUIDE COMPRISING, A SLOT CUT THROUGH THE CONDUCTOR WALL, SAID SLOT DEFINING THE BASE OF A TRIANGLE SHAPED AREA, AND EACH END OF THE SLOT TERMINATING IN AN ADDITIONAL RELATIVELY SHORTER SLOT CUT THROUGH THE CONDUCTOR, EACH OF SAID ADDITIONAL SLOTS EXTENDING PARALLEL TO AN ARM OF THE TRIANGLE SHAPED AREA, BUT TERMINATING SHORT OF THE APEX THEREOF, ALL SAID SLOTS THROUGHOUT THEIR LENGTHS BEING OPEN TO THE SPACE WITHIN THE WAVEGUIDE FOR RF ENERGY TRANSFER BETWEEN SAID SPACE AND THAT OUTSIDE THE WAVEGUIDE. 